The present invention relates to the art of implantable cardiac defibrillators, and in particular, is related to an energy dissipation resistor capable of efficiently and reliably dissipating energy stored in the capacitor(s) of an implantable cardiac defibrillator.
It is often the desire to dissipate electrical energy stored in defibrillator capacitors, rather than discharging to the heart, by diverting the capacitor voltage to an internal resistor. This is commonly referred to as an "internal dump". See, for example, U.S. Pat. Nos. 4,316,472 and 4,488,555 to Imran and Mirowski, respectively, where internal load resistors are shown. Presently, conventional resistive elements, such as carbon or ceramic resistors, and the like are used to dissipate the energy. Such conventional resistive elements tend to be large and bulky, and therefore difficult to package, often requiring extensive incoming inspection processes to assure that a desired reliability is achieved. In addition, although conventional resistive elements have proven generally effective in practice, worst case testing with multiple shock and internal dump episodes has resulted in heating of the resistive element and occasional destruction thereof.
Some types of implantable defibrillation circuitry are disposed on small, light-weight, and flexible printed circuit boards. Consequently, "board real-estate" becomes increasingly important, as does the size, weight, and flexibility of components mounted thereon. It is, therefore, desirable to minimize the size and weight of individual circuit components, while maximizing their structural flexibility to coincide with that of the flexible circuit board to which they are mounted.
Still other types of implantable defibrillation circuitry are disposed on small, light-weight, but rigid printed circuit boards or ceramic substrates. In such cases, it is usually desirable to conserve "board real-estate" while, at the same time, maintaining structural rigidity in the circuit board.